A huge fire raged in Beirut port on Thursday, AFP correspondents said, sparking alarm among Lebanese still reeling from a devastating dockside explosion that disfigured the capital last month.

Thick black columns of smoke rose into the sky, as the army said the blaze had engulfed a warehouse storing oil and tyres.

It was not immediately clear what caused the blaze. "Operations have begun to extinguish the fire and army helicopters will take part," the military said in a statement on Twitter.

Social media users posted video footage, which sparked alarm among Beirut residents only just recovering from the country's deadliest peace-time disaster.

"Insane fire at the port, causing a panic all across Beirut. We just can't catch a break," Human Rights Watch researcher Aya Majzoub wrote on Twitter.

The August 4 explosion of hundreds of tonnes of ammonium nitrate fertiliser at the port killed more than 190 people, wounded thousands and ravaged large parts of the capital.

The blast sparked widespread outrage after it emerged authorities had been aware of the presence of the huge stockpile, and prompted the government to resign.

Human rights researcher Omar Nashabe tweeted: "Where are we living? This is the scene of the crime a month ago! Where is the judiciary? Where is the state? Where is responsibility?"

The port blast piled new misery on Lebanese already battling the coronavirus pandemic and the country's worst economic crisis in decades, which has seen poverty rates double to more than half the population.